1. Field of the Invention
The present invention relates to a method for individually bonding inner leads installed on a tab tape to electrodes of semiconductor elements using a bonding tool.
2. Prior Art
As shown in FIG. 3(a), inner leads (2a, 2b, 2c, 2d) installed on a tab tape 1 project inward from the four sides of a square opening 10 in the tab tape 1 oriented in the X and Y directions such that the inner leads on the four sides are perpendicular to each other. In a known method, the inner leads 2a through 2d of the tab tape 1 are individually bonded to the electrodes 3a of a semiconductor element 3 by applying ultrasonic waves to a bonding tool 4 as seen in FIG. 3(b).
The direction of the ultrasonic vibrations of the horn 5 having the bonding tool 4 in the axial direction of the horn 5. Accordingly, the horn 5 is rotated the axial direction thereof matches the direction in which the inner leads (2a through 2d) project as shown by dotted lines in FIG. 3(a) in order to secure that the ultrasonic waves are evenly applied to the inner leads (2a through 2d).
More specifically, first any positional discrepancy between the inner leads (2a through 2d) and the electrodes 3a is detected by a detection means (not shown), and the positions of the inner leads and electrodes are adjusted to be matched.
The axial directional of the horn 5 is set to coincide with the direction of inner lead 2a-1 (i.e., the Y direction) at the left end of the inner leads 2a. The bonding tool 4 is lowered so that inner lead 2a-1 is pressed against the electrode 3a, and ultrasonic vibrations are applied to the horn 5 so that the inner lead 2a-1 and electrode 3a are bonded.
Next, the bonding tool 4 rises and is moved in the X direction so that the tool 4 is positioned over the next inner lead 2a-2. Then, the inner lead 2a-2 and another electrode 3a are bonded by the same operation as that described above.
When bonding of all of the inner leads 2a is completed, the bonding head (not shown) which holds the horn 5 is rotated 90 degrees so that the axial direction of the horn 5 is coincides with the direction of the inner leads 2b, and the inner leads 2b are bonded in the same manner as the inner leads 2a.
When the bonding of the inner leads 2b is completed, the bonding head is again rotated 90 degrees in order to bond the inner leads 2c, and the bonding of the inner leads 2c is performed. When the bonding of the inner leads 2c is completed, the bonding head is rotates 90 degrees, and the bonding of the inner leads 2d is performed. When the bonding of the inner leads 2d is completed, the bonding head is again rotated 90 degrees so that the bonding tool 4 is returned to the starting position.
Thus, in prior art bonding apparatus, the bonding head must be rotated four times (90 degrees each time) to complete one device.
Thus, since it is necessary to rotate the bonding head four times for each device, considerable time is wasted, and the conventional technique is inferior in terms of productivity. In addition, a rotating mechanism for rotating the bonding head is required. As a result, the bonding head section is complicated, and the over all cost of the apparatus tends to increase.